This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Our NIH funded project (RO1 CA045424) has as one of its aims to employ DFT theory to elucidate radiation damage processes including the role of ion radicals and excited states in these mechanisms. Our project is now investigating the role of excited states in electron and hole induced DNA damage such as strand break formation and sugar radical formation via the use of time-dependent density functional theory(TD-DFT). Theoy is employed to elucidate our experimental results. Recent publications: 1. Review Chapter: DFT Treatment of Radiation Produced Radicals in DNA Model Systems Xifeng Li and Michael D. Sevilla, Chapter in Theoretical Treatment of the Interaction of Radiation with Biological Systems. J. R. Sabin and E. Brandas, Eds., Advances in Quantum Chemistry, Elsevier, Volume 52, 59-88 (2007). 2. Photoexcitation of Dinucleoside Radical Cations: A Time-Dependent Density Functional Study A. Kumar, M. D. Sevilla J. Phys. Chem. B.;2006;110(47);24181-24188 3. Base Release in Nucleosides Induced by Low-Energy Electrons: A DFT Study X. Li, L. Sanche and M. D. Sevilla, Radiation Research, 2006, 165, 721-729. 4. The Guanine Cation Radical: Investigation of Deprotonation States by ESR and DFT A. Adhikary, A. Kumar, D. Becker, M. D. Sevilla, J. Phys. Chem. B.;2006;110(47);24171-24180. 5. Low-Energy Electron Attachment to 5'-Thymidine Monophosphate: Modeling Single Strand Breaks Through Dissociative Electron Attachment Kumar, A.;Sevilla, M. D. J. Phys. Chem. B, 111 (19), 5464 -5474, 2007.